1RM Calculator
Enter the weight you lifted and how many reps you completed to get an estimated one-rep max from two standard formulas, along with a percentage table for programming training loads.
Training Percentages (based on Epley estimate)
| Percent of 1RM | Weight |
|---|
How It Works
A one-rep max (1RM) is the heaviest weight you could lift for a single complete rep. Since testing that directly is fatiguing and carries some injury risk, lifters instead perform a set of a few reps with good form and plug the weight and rep count into a formula that estimates the 1RM from the relationship between reps and fatigue.
This calculator shows two widely used formulas. The Epley formula is
1RM = weight x (1 + reps / 30). The Brzycki formula is
1RM = weight x 36 / (37 - reps). Both formulas assume the set was taken close
to failure with good technique. A rep count that is far from failure will overestimate the
true max.
Worked Example
Say you bench pressed 185 lb for 8 reps. Epley: 185 x (1 + 8 / 30) = 185 x 1.267 = 234.3 lb. Brzycki: 185 x 36 / (37 - 8) = 185 x 36 / 29 = 229.7 lb. The two estimates land within about 5 lb of each other, which is typical. From there, the percentage table shows what 80 percent of that estimated max looks like for planning a training block, for example 80 percent of 234.3 lb is about 187.4 lb.
Where the Two Formulas Pull Apart
Epley and Brzycki agree almost exactly right around 10 reps, both landing on a multiplier of 1.333 times the weight lifted. Below 10 reps, Epley runs a little higher, by roughly 2 to 4 percent in the 3 to 8 rep range. Past 10 reps, that flips: Brzycki starts climbing faster than Epley and pulls further ahead the higher the rep count goes. At 12 reps, Epley gives a multiplier of 1.40 while Brzycki has already climbed to 1.44, a gap of about 3 percent. Keep extending that out and it gets worse fast: Brzycki's formula has 37 minus reps in the denominator, so as reps climbs toward 37 that denominator shrinks toward zero and the estimate shoots toward infinity. Epley has no such cliff and just keeps growing in a straight line, which is part of why the two formulas end up so far apart at higher reps.
This mathematical quirk lines up with a real physiological one: the relationship between reps performed and percentage of your true max gets a lot less consistent from person to person once you go much past about 10 reps. Fatigue, technique breakdown, and cardiovascular limits start to matter as much as raw strength, and those vary too much between individuals for any single formula to model reliably. That is why this calculator caps input at 12 reps, and why a set of 3 to 6 reps will generally give you a more trustworthy estimate than a set of 12.
Frequently Asked Questions
How accurate is an estimated 1RM?
Formula-based estimates are typically within about 5 percent of a true tested max. They are most accurate for sets of 1 to 5 reps and get less reliable as rep count climbs, since fatigue affects lifters differently at higher reps.
Why do the Epley and Brzycki formulas give different numbers?
Both are regression equations built from different sets of lifting data, so they weight the relationship between reps and fatigue slightly differently. They actually land almost exactly on top of each other around 10 reps, run a few percent apart at lower rep counts, and then pull apart quickly past 10 reps. The How It Works section below has the numbers behind this.
Which formula should I trust more?
Neither is definitively more correct. Below about 10 reps, Epley tends to run a little higher than Brzycki. Past about 10 reps, that flips, and Brzycki starts running noticeably higher than Epley. Many lifters just look at both and treat the true value as somewhere in that range, and lean on lower rep sets for a more trustworthy estimate.
What is the training percentage table for?
Strength programs are often written as a percentage of your 1RM, for example 5 sets of 5 at 80 percent. Once you have an estimated 1RM, the percentage table converts that into an actual weight to load on the bar for a given percentage.
Does this work for any exercise?
It works best for compound barbell lifts like the squat, bench press, deadlift, and overhead press, where the reps-to-fatigue relationship is fairly linear. It is less reliable for isolation exercises or machines.
Should I just test my true 1-rep max instead?
A true max attempt carries more injury risk and requires a spotter, a lot of warm-up sets, and a good day. Estimating from a submaximal set you can perform safely is a practical alternative for most training purposes.